NCERT Class 8 Science Book Curiosity Chapter11 QA

Chapter 11 : Keeping Time with the Skies

Questions and Answers (1 Mark)

1. Question: What is a day?
   Answer: A day is the time taken by the Earth to complete one rotation on its axis.

2. Question: What causes day and night?
   Answer: Day and night are caused by the rotation of the Earth on its axis.

3. Question: What is a year?
   Answer: A year is the time taken by the Earth to complete one revolution around the Sun.

4. Question: Name the natural satellite of the Earth?
   Answer: The Moon is the natural satellite of the Earth.

5. Question: What is a lunar month?
   Answer: A lunar month is the time taken by the Moon to complete one revolution around the Earth.

Questions and Answers (2 Marks)

6. Question: Why do we see phases of the Moon?
   Answer: We see phases of the Moon because the Moon revolves around the Earth, and only a part of its sunlit surface is visible from the Earth at different times.

7. Question: What is a solar day?
   Answer: A solar day is the time interval between two successive noons, when the Sun is at the highest point in the sky.

8. Question: Define rotation and revolution?
   Answer: Rotation is the spinning of the Earth on its axis, while revolution is the movement of the Earth around the Sun.

9. Question: Why are shadows shorter at noon?
   Answer: Shadows are shorter at noon because the Sun is almost overhead at that time.

Questions and Answers (5 Marks)

10. Question: Explain how ancient people measured time using the sky?
    Answer: Ancient people observed the movement of the Sun, Moon, and stars to measure time. They used sunrise, sunset, length of shadows, phases of the Moon, and position of stars to estimate days, months, and years. Sundials were used to measure time during the day, while the Moon phases helped in making calendars.

11. Question: Describe the phases of the Moon?
    Answer: The Moon appears in different shapes called phases due to its revolution around the Earth. Starting from the new Moon, the visible part slowly increases to form the crescent, first quarter, gibbous, and full Moon. After the full Moon, the visible part decreases again through gibbous, last quarter, and crescent before returning to the new Moon.

Fill in the Blanks (5 Marks)

12. The Earth completes one rotation in (24) hours.
13. The movement of the Earth around the Sun is called (revolution).
14. The full Moon occurs when the entire illuminated part of the Moon is (visible).
15. A year has (365) days.
16. The shadow is longest in the (morning and evening).

True or False (5 Marks)

17. The Earth rotates from west to east.
    Answer: True.

18. The Moon produces its own light.
    Answer: False.

19. A lunar month is equal to a solar year.
    Answer: False.

20. The Sun appears to move across the sky due to the Earth’s rotation.
    Answer: True.

21. Ancient calendars were based on the movement of heavenly bodies.
    Answer: True.